# 4. Task and order of execution / Завдання та порядок виконання

> **Source of tasks.** The requirements below are taken **exactly** from the
> assignment *"Lab #1: Basic Set Operations"*. Implement the functions with the
> specified behaviour; the input/output examples are authoritative.

## Objective

Implement foundational set operations **without using pre-built libraries or
classes**.

## Requirements

- Sets can contain **integers, strings, or any data type**.
- **Do not use built-in set classes or their methods.** Examples:
  - **C#** — avoid `HashSet<T>`
  - **Python** — do not use `set()`
  - **Java** — avoid `HashSet<E>`
  - **JavaScript** — do not use `Set`
  - …and so on for other languages.

## Order of execution

Implement the tasks tier by tier, and test each function against its examples
before proceeding to the next. Your score corresponds to the **highest tier**
that is fully and correctly implemented.

## Tasks

### Tier 1 — Set creation and manipulation (Score: 60–74)

| Function | Behaviour | Example input | Example output |
|---|---|---|---|
| `createSet(elements)` | Create a set from a list of elements, removing any duplicates. | `[1,2,2,3]` | `[1,2,3]` |
| `addElement(set, element)` | Add an element to the set if it is not already present. | `([1,2,3], 4)` | `[1,2,3,4]` |
| `removeElement(set, element)` | Remove an element if it exists in the set. | `([1,2,3,4], 4)` | `[1,2,3]` |
| `containsElement(set, element)` | Return a boolean indicating whether an element is present. | `([1,2,3], 4)` | `False` |

### Tier 2 — Advanced set operations (Score: 75–89)

| Function | Behaviour | Example input | Example output |
|---|---|---|---|
| `union(setA, setB)` | Return a new set that is the union of the two sets. | `([1,2,3], [3,4,5])` | `[1,2,3,4,5]` |
| `intersection(setA, setB)` | Return a new set that is the intersection of the two sets. | `([1,2,3], [3,4,5])` | `[3]` |
| `difference(setA, setB)` | Return a set of elements in `setA` but not in `setB`. | `([1,2,3], [3,4,5])` | `[1,2]` |
| `complement(setA, universalSet)` | Return the complement of `setA` relative to a universal set. | `([1,2,3], [1,2,3,4,5])` | `[4,5]` |

### Tier 3 — Expression evaluator (Score: 90–100)

`evaluateExpression(expression, setsDict)` — given a string expression and a
dictionary of sets, compute the result of the expression.

**Example**

- Expression: `"A intersection B union C"`
- `setsDict = {'A': [1,2,3], 'B': [3,4,5], 'C': [5,6,7]}`
- Output: `[3,5,6,7]`